That's the standard weight for oats, but generally it actually runs 40 to 46 lbs/bu. The standard weight was built a long time ago before much of the modern seed varieties had been bred.

That said, you're right, it's still a lot lighter to shovel than something like wheat, and glorious compared to faba beans which is like shovelling gravel.

And you're right about the slickness, oats are almost a pleasure to shovel. But the dust is really irritating to the skin, at least to most people. It can be rough to deal with at harvest time.